African-American adolescents are at high risk for HIV and other sexually transmitted diseases. HIV prevention efforts have had limited success with this population. Using naturally occurring social groups such as crowd-based cliques, in the delivery of interventions may lead to improved effects. Advancement in this area is dependent on gleaning more information about African-American neighborhood crowd-based cliques, and on the development of theory-based interventions that incorporate cliques in the study design. We propose to conduct a longitudinal observational study of crowd-based cliques in an African-American neighborhood, and to conduct a pilot test of a theory-based intervention. This work will be conducted in a neighborhood with a large population of adolescents at high risk for HIV/STDs, and will include in- and out-of-school youths. We will: 1. Conduct a 12-month observational study of crowd-based cliques that focuses on characteristics of cliques and relationships among cliquemates, including general communication patterns, sexual behavior, and rates of STDs. 2. Examine the hypothesized determinants of risk-behavior, and mediators of these determinants as predicted by the AIDS Risk Reduction Model (ARRM). We will conduct a pilot test of a new HIV intervention based on the ARRM to evaluate acceptability and feasibility of the intervention in this community. The observational study will include 400 adolescents, age 15-19, from the participating community who will be interviewed four times over a 12 month period. The pilot study will include a three-session intervention based on the ARRM that draws heavily on the work of Jemmott and others. Standard pre- and post-measures, and process measures, will compare the new HIV intervention with a standard health education intervention in a sample of 100 teens. Findings will contribute to the development of future cliquebased HIV interventions based on the AIDS Risk Reduction Model.